</pre>一方面鞏固下AsyncTasK 的用法,另一方面熟悉下基本的網絡操作。<p></p><p>那麼我們一邊實踐一邊學習吧:</p><p>網絡操作必須記得在manifest.xml 加入:</p><p></p><pre name="code" class="html"><uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
1.聯網的方式:
Android 中提供了 HTTPClient 和 HttpURLConnection 兩種方式 二者均支持HTTPS ,流媒體上傳和下載,可配置的超時, IPv6 與連接池(connection pooling)。官方推薦使用HttpURLConnection(Android2.3以上版本,一般我都是用的API14以上,Android4.0)。
2.官方文檔中建議是先檢查網絡連接,當前網絡是否可用
// 檢測當前網絡是否可用
private Boolean testInternet() {
// TODO Auto-generated method stub
// framework層的管理器
ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netWorkInfo = conMgr.getActiveNetworkInfo();
if (netWorkInfo != null && netWorkInfo.isConnected()) {
return true;
} else {
return false;
}
}
3.創建AsyncTask 這裏我暫不貼出代碼,最下面貼出完整代碼。
4.創建downloadUrl() 執行下載html
我們使用 HttpURLConnection 來執行一個
GET 類型的操作並下載數據。在調用 connect()之後,通過調用getInputStream()來得到一個包含數據的InputStream 對象。
// 下載html頁面
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// 這裏只打印char[500]的字符
int len = 500;
try {
URL url = new URL(myurl);
//創建HttpURLConnection對象,打開端口
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//設置讀取,連接超時時間,單位是毫秒
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
//請求方式爲GET
conn.setRequestMethod("GET");
conn.setDoInput(true);
//建立連接
conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
//獲取InputSream
is = conn.getInputStream();
//把InputStream 轉爲 String
String contentAsString = readIt(is, len);
return contentAsString;
} finally {
if (is != null) {
is.close();
}
}
}
注意:getResponseCode()
會返回連接狀態碼( status code). 這是一種獲知額外網絡連接信息的有效方式。status code 是 200 則意味着連接成功.
5.編寫上面的readIt(),把InputStream 轉爲String,方便顯示。
下面貼出完整代碼:
佈局文件:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="${relativePackage}.${activityClass}" >
<EditText
android:id="@+id/et_url"
android:layout_width="match_parent"
android:layout_height="60dp"
android:hint="enter url"
/>
<Button
android:id="@+id/btn"
android:layout_below="@id/et_url"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="download"
/>
<TextView
android:layout_below="@id/btn"
android:layout_margin="20dp"
android:id="@+id/tv_html"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/hello_world"
android:gravity="center"/>
</RelativeLayout>
MainActivity:
package com.zero.httpdemo;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import android.app.Activity;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity {
private static final String DEBUG_TAG = "debug";
private TextView tv;
private Button btn;
private EditText et;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
getWindow().requestFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
tv = (TextView) findViewById(R.id.tv_html);
btn = (Button) findViewById(R.id.btn);
et = (EditText) findViewById(R.id.et_url);
btn.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
if (testInternet()) {
String urls[] = {"http://"+et.getText().toString()};
new DownloadWebPage().execute(urls);
} else {
Toast.makeText(getApplicationContext(),
"Can't connect Internet!", Toast.LENGTH_SHORT)
.show();
}
}
});
}
private class DownloadWebPage extends AsyncTask<String, Integer, String> {
@Override
protected String doInBackground(String... urls) {
try {
return downloadUrl(urls[0]);
} catch (IOException e) {
return "URL may be invalid.";
}
}
@Override
protected void onPostExecute(String result) {
tv.setText(result);
}
}
// 檢測當前網絡是否可用
private Boolean testInternet() {
// TODO Auto-generated method stub
// framework層的管理器
ConnectivityManager conMgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netWorkInfo = conMgr.getActiveNetworkInfo();
if (netWorkInfo != null && netWorkInfo.isConnected()) {
return true;
} else {
return false;
}
}
// 下載html頁面
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// 這裏只打印char[500]的字符
int len = 500;
try {
URL url = new URL(myurl);
//創建HttpURLConnection對象,打開端口
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
//設置讀取,連接超時時間,單位是毫秒
conn.setReadTimeout(10000);
conn.setConnectTimeout(15000);
//請求方式爲GET
conn.setRequestMethod("GET");
conn.setDoInput(true);
//建立連接
conn.connect();
int response = conn.getResponseCode();
Log.d(DEBUG_TAG, "The response is: " + response);
//獲取InputSream
is = conn.getInputStream();
//把InputStream 轉爲 String
String contentAsString = readIt(is, len);
return contentAsString;
} finally {
if (is != null) {
is.close();
}
}
}
// 把InputStream 轉換爲字符串,顯示在TextView中
public String readIt(InputStream stream, int len) throws IOException,
UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
}
如果對AsyncTask還不熟悉,可以看我上一篇blog哦!
效果圖: